this post, after Sony first announced their new handheld gaming device.
Let's look at the hardware specs first. The 3DS has a 3.5" 400 x 240 screen on top (that's 3D mode resolution; it would be 800 x 240 in 2D) and the second screen below is 320 x 240. The PS Vita has a single 5" screen with a resolution of 960 x 544. The iPhone 4 (and likely the iPhone 5) has a 3.5" screen with a resolution of 960 x 640. The PS Vita has the largest screen that's close to the highest resolution screen, which is the iPhone screen. The 3DS has the glasses-free 3D effect which none of the other devices have, but for about 15% to 25% of the customers the 3D effect either doesn't work or produces nausea and headaches, or is just unpleasant.
What about graphics performance? Clearly the PS Vita, with its quad-core ARM A9 CPU and Power VR graphics co-processor has the others beat. The iPhone 4 has a single-core ARM-based A8 CPU, but the iPhone 5 is likely to have the same A9-based dual core CPU that the iPad 2 has. It still won't be up to the performance of the PS Vita, but it won't exactly be a sluggard, either. The 3DS has some custom silicon in there, so it's hard to say for sure how it compares. According to this article, the 3DS can put out about 30 million triangles per second, about the same as an iPhone 3GS and slightly less than a PSP. Which means it's way, way behind a PS Vita or an iPhone 5, by about an order of magnitude I'd guess. The fillrate in pixels per second is about 1.6 billion for the 3DS, which is definitely better than the PSP at 664 million or the iPhone 3GS at 500 million... but certainly way behind the PS Vita or the iPhone 5 (the iPhone 4 has a raw fillrate of at least 700 million pixels).
Finally, there's the price point comparison: The 3DS is $249, the iPhone 4 is hard to compare since it's under a contract, but you can get an 8 GB iPod Touch for $229, and the PS Vita will be $249.
I have to say that the 3DS doesn't stack up well at its current price point. Certainly its sales have been weaker than Nintendo projected, and it's currently limping along at a fairly low level. Nintendo is hoping that some strong software titles and more marketing spending will bring up its sales, but I think Nintendo will have to cut the price to $199 before Sony launches the PS Vita, or shortly thereafter.
Nintendo's big edge with the 3DS was to have been the 3D effect, but that's gotten a mixed reception from customers. Even Nintendo has been busy de-emphasizing its importance. Without that, thought, the 3DS doesn't have any advantages over the competition aside from exclusive software titles. Which is no small advantage, as Link and Mario and Starfox and others are a huge draw. It may not be enough for Nintendo to overcome the hardware and business model advantages of iPhones, the PS Vita, and of course Android smartphones and tablets. There are far more mobile gaming options than ever before, and smartphones and tablets have a variety of other features that make them extremely attractive.
Sony seems to be working towards having a variety of inexpensive downloads for the PS Vita, as well as movies, and perhaps will be more open to other functionality. Nintendo has said they will have 3D movies available, but 3D movies aren't doing all that well at the box office either. The 3D fad may have run its course... which would be a bad thing for Nintendo since it planned for 3D to be the major selling point of the 3DS (hence the name!).
The iPhone (and Android smartphones) have suffered from a lack of top-quality games, but titles like Infinity Blade have shown that it's possible to do some very impressive games for the hardware. (And with Epic Games announcing they've brought in more than $10 million dollars from Infinity Blade, it's clear you can make real money from these games, too.) I expect we'll see more high-quality games for smartphones in the coming years.
Verdict: On the raw hardware level, the PS Vita has the horsepower, the biggest screen and the best array of features. The iPhone/iPod Touch has an impressive variety of apps, many of them free, and quite decent hardware performance even though it lacks dedicated gaming controls. The 3DS is bringing up the rear right now, but with better software and a lower price point it could be quite competitive. Nintendo may well release a sleeker, less expensive version next year, and then it will be a different story.